(1) Field of the Invention
The present invention relates to a holding structure for spectacle lenses, and more particularly, to a spectacle lens holding structure suited for use in rimless spectacles.
(2) Description of the Related Art
In recent years, rimless spectacles have been attracting attention because of their advantages such as wide field of view and lightness in weight. Rimless spectacles are classified into two types, that is, a type called semi-rimless spectacles in which lenses are suspended by means of nylon thread wound round the lower edges thereof, and a type called two-point or three-piece type in which lenses are supported by means of screws fitted into holes formed through the lenses. In the former type of lens holding structure, an upper edge portion of each lens is fitted in a metal part, a nylon thread is laid along a groove cut in a lower edge portion of each lens, and the opposite ends of the thread are fastened to the upper metal part, whereby the lenses are suspended. In the latter type of lens holding structure, small screw holes of about 1.4 mm in diameter are bored through portions of each lens close to the right and left edges thereof, respectively, and screws are inserted through the holes to attach the lenses to lens holding members such as a bridge, endpieces, straps, etc. (see Unexamined Japanese Utility Model Publication No. 4-63419 and Unexamined Japanese Patent Publication No. 63-6521, for example).
In the conventional holding structure for the semi-rimless spectacles, however, each lens must first be ground so that the peripheral edge thereof may be flat, and then a groove must be cut along the entire peripheral surface (edge surface) of the lens. Thus, in the case of a lens with a small thickness, considerable skill is required to cut a groove, and the thickness between the groove and the lens surface may become so small that the lens may be chipped when the spectacles are dropped.
In the holding structure for the two-point or three-piece type spectacles, screw holes must be formed through each lens. Therefore, when a screw hole is bored from one side to the other of the lens, the edge of the open end on the other side of the lens may be chipped, making the machining difficult. Further, the lens may crack when a screw hole is bored; therefore, screw holes must be formed at a distance from the edge of the lens. If, however, screw holes are formed at a distance from the edge of the lens, a problem arises in that the screw holes and holding sections associated therewith obstruct the field of view. Further, since lens holding members such as screws and nuts protrude from both surfaces of the lens, they form an obstacle when the lens surfaces are wiped up.
Furthermore, it is necessary that the screw holes be bored perpendicularly or obliquely with respect to the lens surface. Also, the screw holes must be bored at accurate positions with respect to the edge of the lens so that an endpiece or a bridge can be firmly fixed, but since the lens has a spherical surface, the drill bit can easily slip off along the spherical surface of the lens, requiring a great deal of skill in the machining.